A microcomputer having a debugging support function includes a debugging interface for carrying out a communication with an emulator or a host computer in the debugging. For example, a serial input/output interface based on a JTAG (Joint Test Action Group, IEEE std 1149.1, IEEE Standard Test Access Port and Boundary-Scan Architecture) protocol is used for the debugging interface. Patent Document 1 has also described a microcomputer having such a debugging interface.    Patent Document 1: JP-A-2002-202900 (Paragraph 0017)